new rpm sensor

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labview1958
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new rpm sensor

Post by labview1958 » Fri Sep 09, 2005 11:20 am

I have made a new rpm sensor. Here it is. Any comments?<p>Image

Newz2000
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Re: new rpm sensor

Post by Newz2000 » Fri Sep 09, 2005 12:16 pm

Have you built it? Does it work? When you put it together on your breadboard, what readings do you get?<p>What is it supposed to do? What is it doing that is contrary to what you want it to do?<p>Can you be more specific with your question? "Here it is. Any comments?" is kind of vague. If in doubt, read this article about how to ask questions.<p>To paraphrase from the article, what you're doing is putting the work on the people whom you're trying to get help from. Instead of making people play 20 questions with you, do the experiment, blow up a few ICs and ask for help when you run into a snag.<p>Just my $0.02 worth. I'll sit down now.<p>[ September 09, 2005: Message edited by: Matt Nuzum ]</p>

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Chris Smith
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Re: new rpm sensor

Post by Chris Smith » Fri Sep 09, 2005 1:12 pm

Nope, no comments.

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jwax
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Re: new rpm sensor

Post by jwax » Fri Sep 09, 2005 1:43 pm

Comments?
Just how thick headed are you?
That's all.

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philba
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Re: new rpm sensor

Post by philba » Fri Sep 09, 2005 5:15 pm

Comments? yes but first a question - why do you use image shack??? the images are often barely readable and sometimes completely unreadable. To make it worse, that stupid "punch osamma" pop under is really annoying. Especially since it seems to beat mozilla's pop-up blocking.<p>comment - I agree with matt. you need to be asking "why does it work this way or why doesn't work the way I think. Not - will this work? <p>Frankly, you don't seem to be learning anything other how to get free help. A lot of us here have put lots of effort into learning electronics and I don't mind sharing but it's a little frustrating to get questions that appear to be asking for a completed solution for you to go build. If you can't dive in and just try things, I suggest you stick to kits that have already worked out the design issues for you.

Robert Reed
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Re: new rpm sensor

Post by Robert Reed » Fri Sep 09, 2005 5:26 pm

First thing I see is a 2K resistor in series with a 220k resistor for no apparent reason. 220 K is a 5% (at best) standard resistor with an acceptable value of 209K to 231K. The 2K resistor gets nested in there without notice. The whole package is too high in value for anything you would want to measure, other than very slow signal rate--another point you neglect to mention. It seems like instead of designig circuits, you are just throwing components together without any thought and then casting them into the wind for other peoples thoughts, You would be much further ahead on this forum to analyze your circuit a little more before posting. And Labview, A little more info on the intended use would also be very helpful.

labview1958
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Re: new rpm sensor

Post by labview1958 » Sat Sep 10, 2005 2:06 am

Thanks. I try to ask smart questions. All of you are a great help. I have learned many things from you.<p>I am trying to make a circuit to find the rpm of a rotating disk that moves at less then 100 rps. It should have a ttl output that is fed into a PC via a ni-6025E daq card. I have a labview program to work out the rpm.<p>Regarding image shack, it is free and I do not have much money. Anyway if you click on the image, it would enlarge and you have a clearer picture.<p>Sorry for the inconvenience.

rshayes
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Re: new rpm sensor

Post by rshayes » Sat Sep 10, 2005 2:32 am

The load resistor (220K) on the phototransistor may be on the high side. If there is any ambient light, the transistor might saturate and not pick up changes in light at all. This value is also so high that the input bias current on the LM319 might become significant.

Robert Reed
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Re: new rpm sensor

Post by Robert Reed » Sat Sep 10, 2005 9:02 am

Much better Labview. The chip numbers have no real meaning as they are not EIA certified, but in looking at the circuit, it looks like you are feeding the photo transistor out put into a comparator with a trip point of ~1.7 V. The hysteresis (470K) looks a bit on the large side, but may get you by if the cicuit is relatively noise free and has clean switching. As to the 220K load for PT output,even though 100 Hz is a low frquency output, you may want to reduce this somewhat. A quick "scope check would confirm this once you are up and running.<p>[ September 10, 2005: Message edited by: ROBERT REED ]</p>

jimandy
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Re: new rpm sensor

Post by jimandy » Sat Sep 10, 2005 11:51 am

I will again show my preference for using Schmitt trigger IC gates. Without actually working it out, I think you could reduce the number of variables (AKA resistors) and be assured of clean sharp pulses.
"if it's not another it's one thing."

terri
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Re: new rpm sensor

Post by terri » Sat Sep 10, 2005 12:09 pm

I went through this a while ago with the questions on cutters. Turned out the querent was cutting sections out of termite hills for some research or other. Put a whole different light on the query!<p>One of the most important aspects of questioning on this forum is to state your application, that is, to tell what are you trying to accomplish.<p>
In labview's query on temperature sensors, he did not mention, until several posts later, that he was trying to measure LN2 temperature. OK. But what for? Was he just trying to build a level sensor? To check for impurities? To calibrate a sensor for other cryo-applications? <p>
The significant fact that he was reaching down to LN2 temps only came out after I posted information on the LM34 series of temperature sensors. Gee, did I feel like a fool for wasting my time researching transducers 'way, 'way up in the -50dF to 300dF range! <p>
Frankly, that's why I "escape" from this board for long periods.... just frustration with the badly-posed questions.<p>
Just my US$ 0.20. (Inflation, doncha know.)<p>[ September 10, 2005: Message edited by: terri ]</p>
terri wd0edw

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Chris Smith
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Re: new rpm sensor

Post by Chris Smith » Sat Sep 10, 2005 1:31 pm

I agree,....When a person poorly asks a question the proper etiquette is to ask them why, and leave it at that. <p>If they see their folly, they proceed with more details, if they don’t you only need answer with what’s in front of you, and in this case it was zero or close to it. <p>Equal parts of participation are required here.

labview1958
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Re: new rpm sensor

Post by labview1958 » Sun Sep 11, 2005 2:08 am

Can the LM319 be considered as a schmitt trigger?

jimandy
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Re: new rpm sensor

Post by jimandy » Sun Sep 11, 2005 5:14 am

Technically a Schmitt trigger is a circuit with hysteresis (Google up the word if you're not famililar with the term).<p>In the family of logic IC's, several have been configured internally to provide the "snap action" that hysteresis provides which makes for good signal conditioning where sharp edges are required. OpAmp circuits can be designed to do that but you can emlininate some resistors by using a 7414 or 74132 IC or the CMOS equivalents. If you don't have it, you should get a copy of Don Lancaster's CMOS Cookbook for more info.
"if it's not another it's one thing."

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MrAl
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Re: new rpm sensor

Post by MrAl » Sun Sep 11, 2005 7:36 am

Hi there,<p>As others have mentioned, you dont need the
two resistors in series but can get away with
one 220k resistor instead.<p>Also, a schmitt trigger is a circuit that
has hysteresis, and since your LM319 is
connected with resistors that provide a small
amount of positive feedback, your LM319 circuit
becomes a schmitt trigger.
The advantage of creating your own ST circuit
over using an ic that is already a ST is that
you can adjust the amount of hysteresis by
changing one or more of the external resistor
values. For example, to add more hysteresis
you can lower the value of the 470k resistor
or increase the 10k to 20k, or do both. This
will provide more noise immunity.
The LM319 comparator ic is a good choice, but
from what you say i think you mentioned that
the max rps is 100? In that case the ic only
has to work up to about 100 Hz and almost any
comparator chip can do that. The LM339 is a
cheap chip and you get four to a package.<p>Im also assuming there isnt any ambient light
that can interfere with the reflected light
getting to the sensor.<p>If you like, you can increase resolution by
providing multiple reflective surfaces instead
of one. For example, if you provide four
surfaces your circuit will output four pulses
for every revolution instead of just one.
Of course your pc has to keep up with the
faster pulse train, but then you can measure
approximately every 1/4 turn.
If you make one surface slightly wider than
the others and measure pulse width with the pc,
you'll know when you've reached top dead center.<p>
Take care,
Al
LEDs vs Bulbs, LEDs are winning.

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